To remove impurities from drinking water, standalone point of use water purification devices, such as pitcher purifiers or countertop units, utilize flowthrough filter media normally packaged in replaceable filter cartridges fitted inside the devices. Ion exchange and activated carbon is a typical flowthrough filter media.
As the water of a batch of water needing treatment passes through the filter cartridge of a standalone point of use water purification device, it contacts the ion exchange and activated carbon filter media, which absorbs impurities from the water flowing therethrough. The quantity of filter media contacted by the water and the water flow rate determine the absorption efficiency. Typically, filter cartridges having elongated profiles deep enough to allow pollutants to be absorbed by the filter media in the time it takes the water to flow through the filter have been employed.
The ion exchange and activated carbon filter media is contained in the elongated filter cartridges as a bed of closely-packed beads or grains, with a consistency of sand or coffee grounds. As the water flows therethrough, it takes the path of least resistance and makes its own channels through the filter bed. Such “channeling” action, however, leads to the undesirable result that “impurities” seep through the filter cartridge along with “purified” water, since the water that flows through the channels does not contact the filter media for enough time to allow effective absorption to take place.
To insure repeatable operation after use, the ion exchange and activated carbon filter media needs to remain wetted. In the usual case, this requirement has necessitated that the user take steps to insure the standalone point of use water purification device always contains enough water to keep the filter cartridge fitted therein at least partially submerged in water.